Epidemiologic and clinical studies provide strong evidence that gonococcal and chlamydial infections facilitate the transmission of HIV infection and that control of gonorrhea and chlamydia needs to remain high on the agenda of HIV control programs. In addition, the high prevalence of gonococcal and chlamydial co-infection may further increase the risk of HIV transmission. Yet despite these clinical observations, few studies have examined the biology of co-infection nor how these microbes might interact when in the same mucosal environment. It is toward the examination of the biological mechanism of enhancement of co-infection that this proposal is directed. Our studies have shown that exposure of human reproductive tract epithelial cells to gonococci and chlamydia induced the release of proinflammatory cytokines including IL-1, IL-6, and TNF-alpha, which may activate quiescent T cells, alter susceptibility of resident activated T cells and macrophages, and recruit immune cells that are targets for HIV-1 infection thereby enhancing HIV-1 infection or replication. In support of this concept, we provide preliminary data which indicates that gonococcal LOS and culture supernatants taken from reproductive tract epithelial cells infected with C. trachomatis induced HIV-1 expression in the latently-infected promonocytic cell line U1. Given that gonococcal and chlamydial infections enhance HIV infection or replication, strategies that prevent gonococcal and chlamydial should have an impact on HIV-1 transmission as well. One such approach is the development of topical microbicides for vaginal or rectal application that could prevent the invasion at mucosal surfaces. Identification of novel microbicides or alternative therapeutics requires an understanding of the molecular interactions of STI pathogens during co-infection at mucosal surfaces. To this end, we will evaluate the mucosal innate immune response to gonococcal and chlamydial infection using human cell culture systems important in the genital and intestinal tract and determine whether changes in the mucosal environment enhance HIV infection. The Specific Aims are: 1) to characterize the innate immune response to invasion of reproductive tract and intestinal epithelial, endothelial, and dendritic cells by gonococci and chlamydia in terms of the production of cytokines and defensins through engagement of TLR and TREM receptors; 2) to determine the effect of stimulation of innate immune responses by gonococcal and chlamydial invasion on HIV-1 infection of quiescent and activated T cells and macrophages; 3) to define the signal transduction events involved in the expression of innate immune response cytokines and defensins in response to invasion of epithelial cells by gonococci and chlamydia.